can you still use the sounds if the game you are making is intended to be sold, i.e. shareware?

Because it looks like the cc legal agreement specifies that it can not be used for any commercial purpose.

"You are free: To sample, mash-up, or otherwise creatively transform this work for commercial or noncommercial purposes.

Under the following conditions: You must attribute the work in the manner specified by the author or licensor (but not in any way that suggests that they endorse you or your use of the work)."

The only real limitation involving the recordings is the restriction of using an entire sample "as is" for commercial purposes. The recordings must be "sampled, mashed-up, or otherwise creatively transformed," though there is currently some unspoken leeway involving creative transformation. If you sync the sound of an explosion to a visual of an explosion, for example, I don't think most authors here expect any creative transformation beyond that, but see The Future License of Freesound for clarification of that, because for your purposes you are correct, simple synching is not allowed under Sampling Plus 1.0.

But if you contact the authors of the files you want to use, I'm sure most would grant permission to sync their sound effects.